Moscow on Saturday accused the chemical weapons watchdog of manipulating the results of its investigation into the poisoning of a former Russian spy, saying his samples had traces of a nerve agent used by the west.
The news which has been hailed as a significant milestone, comes just over a month after the pair were found slumped over on a park bench in the English city, after they were poisoned by a deadly nerve agent.
Police have said that the highest concentrations of the Novichok nerve agent were found on Mr Skripal's front door, suggesting that was where the nerve agent had been deposited.
The independent scientists from the Organization for the Prohibition of Chemical Weapons (OPWC) have confirmed Thursday that the nerve agent Novichok was used in Salisbury, England on March 4 in a chemical attack on former Russian spy Sergei Skripal and his daughter.
"It is highly likely that the Russian intelligence services view at least some of its defectors as legitimate targets for assassination", he said.
Sir Mark also identified the key institute for developing Novichok in the former Soviet Union as a branch of the State Institute for Organic Chemistry and Technology near Volgograd. British Prime Minister Theresa May has said it is highly likely that Moscow was behind the attack.
"In 2017, we eliminated all chemical weapons", Yakovenko said.
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Western diplomats said they were ready to allow time for negotiations to make every effort to bring Russian Federation aboard. McKenzie defended the attacks in response to questions about the proof that Assad had used chemical weapons on civilians.
She is in the care of "trained officers" who are taking her through the investigative process.
"The codeword for the offensive chemical weapons programme (of which Novichoks were one part) was FOLIANT", he said. "Within the last decade, Russian Federation has produced and stockpiled small quantities of Novichoks under the same programme", he said.
Asked if Russian Federation would open up the Shikhany institute for an OPCW inspection, Yakovenko said Russian Federation didn't produce or stock Novichok "so why should we invite [inspectors] because our official position is like that?"
"There are over 100 British journalists here, why are none of you calling to meet Miss Skripal - not a single person?"
The embassy believes that Sedwill's letter published on April 13 is "yet another confirmation there exists no proof of Russia's alleged involvement in the Salisbury incident".
She also said she would give interviews to the media in time, but asked the press to have patience while she recovers.
The Russian embassy, which has repeatedly demanded access to the Skripals, cast doubt on the authenticity of her statement Thursday.